During the past years, the interest in using mobile and landline/wireline computing devices in day-to-day communications has increased. Desktop computers, workstations, and other wireline computers currently allow users to communicate, for example, via e-mail, video conferencing, and instant messaging (IM). Mobile devices, for example, mobile telephones, handheld computers, personal digital assistants (PDAs), etc. also allow the users to communicate via e-mail, video conferencing, IM, etc. Mobile telephones have conventionally served as voice communication devices, but through technological advancements they have recently proved to be effective devices for communicating data, graphics, etc. Wireless and landline technologies continue to merge into a more unified communication system, as user demand for seamless communications across different platforms increases.
To accommodate the new and different ways in which Internet Protocol (IP) networks are being used to provide various services, new active measurement techniques are being developed and standardized to verify the service performance. Knowing how much capacity is available in real-time on a path (congested or not) across one or more IP networks is valuable information to the network operators or application users. Measurements of available path capacity can be used for network characterization and application performance estimation. The capability of estimating available capacity, end-to-end, over a data transfer path of a data communication system comprising a data network is useful in several contexts, including network monitoring and server selection. Passive estimation of available capacity of a data transfer path, such as estimation of bandwidth of an end-to-end data transfer path is possible in principle, provided all network nodes in the data transfer path can be accessed. However, this is typically not possible, and estimation of available end-to-end capacity of the data transfer path, is typically done by active probing of the data transfer path. The available capacity such as bandwidth can be estimated by injecting data probes into the data transfer path, and then analysing the observed effects of cross traffic on the probes. This kind of active measurement requires access to sender and receiver hosts, typically data network nodes, only, and does not require access to any intermediate nodes in the data transfer path between the sender and receiver nodes.
Conventional approaches to active probing require the injection of data probe packet traffic into the data transfer path of interest at a rate that is sufficient transiently to use all available capacity, and cause induced transient congestion of the data transfer path being estimated. If only a small number of probe packets are used, then the induced transient congestion can be absorbed by buffer queues in the nodes. Accordingly, no data packet loss is caused, but rather only a small data path delay increase of a few data packets. The desired measure of the available capacity is determined based on the path delay increase. Probe packets can be sent in pairs or in trains, at various rates, also referred to as probing rates. The probing rate where a data path delay begins increasing corresponds to the point of congestion, and thus is indicative of the available capacity. Probe packets can also be sent such that the temporal separation between probe packets within a given probe packet train varies, so each probe packet train can cover a range of probing rates.
Methods using active probing are based on a model where probe packets are sent from a sender node to a receiver node in a data communication system. Typically, time stamps of the probe packets at the sender and receiver nodes are then used by an algorithm to produce estimates of the capacity of the data transfer path.
IP-layer performance metrics such as the Available Path Capacity (APC) have been defined in several standard bodies including the Internet Engineering Task Force (IETF) “Defining Network Capacity” Request For Comments (RFC) 5136, and International Telecommunication Union-Telecommunication (ITU-T) Recommendation Y.1540. The IP-layer APC is defined as the capacity available for others to use between a source host and destination host for a given packet type known as type-P packet corresponding to a transport protocol, port number, packet size and Diffserv Codepoint (DSCP).
The IETF IP Performance Metrics (IPPM) working group has defined two IP active measurement protocols: One-Way Active Measurement Protocol (OWAMP), RFC4656, and Two-Way Active Measurement Protocol (TWAMP), RFC5357. OWAMP is designed for measuring one-way packet delay and one-way packet loss between two hosts. TWAMP is based on OWAMP. TWAMP is designed for measuring one-way and two-way, i.e. round-trip, packet delay and packet loss between two hosts.
The basic operation of TWAMP is to let a sender node inject test packets towards a reflector node. When the reflector receives a test packet it is transmitted back to the sender node as soon as possible. Each test packet is time stamped upon transmission and arrival, both at the sender node and reflector host node, so 4 time stamps are produced for each packet.
The original TWAMP is not capable of measuring capacity metrics, such as APC on both the forward and reverse path, since capacity estimation methods need to send and receive trains, where each train is sent at a specific transmission rate in a given direction. This is resolved in IETF RFC 6802 on Ericsson TWAMP Value Added Octets. It introduces a buffering feature in the TWAMP reflector. The reflector node receives and stores all packets in a train before sending them back to the sender node as a new train with a reverse rate, which can be chosen independently of the forward rate, as illustrated in FIG. 1.
Examples of two known methods for estimating capacity of a data transfer path used today, the so-called Trains Of Packet Pairs (TOPP) and Bandwidth Available in Real Time (BART) methods will be explained in detail and how they are related to the present disclosure under section “DETAILED DESCRIPTION”. The BART method can be regarded as an improvement of the TOPP method. See European Patent 1952579 for a further description of the BART method.
Some known solutions for estimating capacity of a data transfer path used today either do, in some situations, not produce real time estimates of available capacity, or do not produce sufficiently accurate estimates of the available capacity of the data transfer path, or both due to non-linear capacity behaviour of the data communication system.